Burner with low porosity burner deck

ABSTRACT

A gas burner ( 10 ), preferably a premix burner, comprising a support ( 12 ) which has a central gas inlet port for supply of gas into a gas supply chamber. The gas supply chamber is enclosed by a perforated metal plate ( 22 ). The perforated metal plate is connected at the bottom to the support through a base section. The perforations in the perforated metal plate provide a burner deck ( 20 ). The burner deck has an overall porosity which is equal to or lower than 11%. The present invention also provides use of this burner, e.g. in heat exchangers.

TECHNICAL FIELD

The present invention relates to a premix burner, more in particular aburner having a flameholder made of perforated metal plate material.Preferably, the burner is a tubular burner having a cylindrical shape.These burners are especially suitable for use in combustion boilers.

BACKGROUND ART

One known type of premix burner consist of one or more of the followingcomponents: a) an end cap located at the top of the burner, b) a burnerdeck, the burner deck consists of a blind piece at the bottom, aperforated piece, with a regular (circular) pattern, with sometimeslocally an additional modification for ignition purposes, in the centrepart and a blind piece at the top. The pattern is mostlycircumferential, and mostly repeating itself in height after a pitch of1-10 mm; c) a distributor, having a blind piece at the bottom, aperforated part in the centre and a blind piece at the top; d) adistributor end cap; e) a flange; f) an anti noise tube which is adevice located in or nearby the flange to adjust the pressuredistribution. Such premix burners are described in e.g. EP 1337789,EP2037175, WO2009/077333, WO2009/065733, WO2009/059933. As can be seenin most of above referenced documents, these burners are provided withdevices in the mixing chamber, such as e.g. an inner liner, also calleddistributor and/or anti-noise tube or other devices such as swirls orperforated disks in or nearby the flange. These devices are needed forstabilization of flames on these burners, which has an effect on noiseand emissions. The need of using these devices implies a considerablecomplication for making the burner and for the assemblage and implies aconsiderable cost.

DISCLOSURE OF INVENTION

The object of the present invention is to obviate the drawbacksmentioned above.

An object of the present invention is to provide a premix burner whichdoes not need such devices in the mixing chamber of the burner to obtaina good stability of the flames and to reduce or even eliminate noiseproblems.

A further object of the present invention is to provide a premix burnerwith a good stability over the full operating range of high to low CO₂,and for the full band of customary or natural gas qualities.

This full band of customary and natural gas qualities covers all gasesselected from hydrocarbons such as methane, ethane, propane, butane,ethene, propene, butene, acetylene, and the like. In contrast with WO95/23315, the present invention does not relate specifically to highreactive fuel gases, which are a mixture of hydrogen and customary fuelgases.

A further object of the present invention is to provide a premix burnerproducing low NOx levels.

An aspect of the claimed invention provides a gas burner preferably apremix burner, comprising a support having a central gas inlet port forsupply of gas into a gas supply chamber. The gas supply chamber isenclosed by a perforated metal plate. The perforations in saidperforated metal plate providing a burner deck. The perforated metalplate is connected at the bottom to the support through a base section.The burner deck has an overall porosity which is equal to or lower than11%, preferably lower than 10%, even more preferably lower than 9%.

In a further aspect, the present invention provides a gas burner asdescribed above wherein the burner further comprises an end capconnected to the perforated metal plate substantially opposite to saidgas inlet port.

In a preferred aspect, the present invention provides a gas burner asdescribed in paragraph 8, wherein the end cap is also provided withperforations. These perforations thereby enlarge and are part of theburner deck. In a preferred aspect, the end cap is made of metal platematerial. In a further preferred aspect, the perforation patterns in theend cap and in the perforated metal plate are equal. In an alternativefurther aspect, the perforation patterns in the end cap and in theperforated metal plate are different. In a further preferred aspect, theperforations, such as e.g. slots and holes, in the end cap and in theperforated metal plate are equal. In an alternative further aspect, theperforations in the end cap and in the perforated metal plate aredifferent.

Conventional premix burners have a porosity in the range of 14 to 18%.It was surprisingly found that lowering the porosity of the burner deckdecreased acoustic time-lag of the flames formed on the burner deck,which enabled us to make a burner which did not need a diffuser anymore.It was also surprisingly found that this burner had an unstable burningwhen this burner was operated in open air, but when applied inside aheat exchanger, this burner had a stable flame and burning pattern. Thisburner also had a more stable response on the first Helmholtz resonanceof the heat exchanger and its peripheral parts, which therefore madethat the burner did not provoke low frequency thermo-acousticinstabilities, often referred to as humming. However, during startsequences under cold conditions with this burner build in, the boilersometimes suffered a humming sound which sometimes makes the burnerstill needing an anti-noise device in its mixing chamber. The use of theanti-noise device in this burner also has a positive effect on the COemission. Also it was found that lowering the porosity did not dampenthermo-acoustic instabilities with a higher frequency than the firstHelmholtz resonance of the boiler, often referred to as whistling orhowling. To cancel these frequencies, the anti-noise device wasnecessary again.

In a further aspect of the present invention, the gas burner of the typedescribed above has a burner deck wherein more than 50% of the burnerdeck has a porosity being equal to or lower than 9% and wherein upto 50%of the burner deck has a porosity being higher than 11% and with anoverall porosity which is equal to or lower than 11%. This modificationof the perforation pattern of the burner deck provided a burner which,next to the effect of the deletion of the diffuser and the removal ofthe humming noise, also had a more stable response on the second andhigher Helmholtz or instable acoustic resonances of the heat exchanger,which therefore made that the boiler, with this build in burner did notprovoke a whistling sound anymore. Next to that, during start sequencesunder cold conditions, the humming sound was eliminated and thereforethe use of anti-noise devices in the mixing chamber of the burner couldbe omitted. Furthermore, this provided a stabilized deck over the fulloperating range of high to low CO₂, and for a broad range of gasqualities.

Another aspect of the claimed invention provides a gas burner asdescribed in [0007], [0008], [0009] or [0011] wherein the burner deckhas different patterns of perforations. Adding more patterns withdifferent pitches showed an increased stability for a broader range ofgas qualities and induced less NOx-emissions. In a preferred aspect, theburner is provided with an abrupt and stepwise variation of theperforation pattern in the burner deck.

In a preferred aspect, the present invention provides a burner withgradually increasing or decreasing perforation pattern or graduallyincreasing or decreasing pitches in between the perforation pattern ofthe burner deck. This grading can go in axial or circumferentialdirection. Gradually increasing or decreasing the perforation of thedecks allows an almost step less variety of the perforation, and thuscreating a varying perforation of the surface of the deck. In anotherpreferred embodiment of the present invention, the burner has acompletely random deck with no repeatability over the full height orcircumference of the burner deck which provides a stabilized deckwithout the additional devices as mentioned above.

Most preferably, in order to improve flame stability, there is adecreased porosity when going downstream. In an embodiment, the partwith a porosity higher than 11% is closest to the gas inlet. The partwith a porosity equal to or lower than 9% is most remote, i.e.downstream, from the gas inlet.

Definitions

The term “burner deck” is to be understood, in the light of thisinvention, to be that part of the burner where the totality ofperforations are present. In case two or more distinct regions ofperforations can be detected on the burner surface, the burner deck isdefined as being the surface spanning of all regions with perforations.

The term “overall porosity of the burner deck” is to be understood, inthe light of this invention, as ratio of the surface of the holes, slotsor other openings divided by the surface of the burner over which theperforated part(s) is(are) located.

The term “perforation pattern” is to be understood, in the light of thisinvention, to be a recurring scheme of perforations.

BRIEF DESCRIPTION OF DRAWINGS

Example embodiments of the invention are described hereinafter withreference to the accompanying drawings in which

FIG. 1 shows an example embodiment according to a first aspect of thepresent invention.

FIGS. 2A and 2B show an example embodiment according to a second aspectof the present invention. FIG. 2C shows an example perforation patternaccording to a second aspect of the present invention.

FIG. 3 shows an example embodiment according to a third aspect of thepresent invention.

FIG. 4 shows an example embodiment according to a further aspect of thepresent invention.

FIG. 5 shows an example embodiment according to a further aspect of thepresent invention.

FIG. 6 shows an example embodiment according to a further aspect of thepresent invention.

FIG. 7 shows an example embodiment according to a further aspect of thepresent invention.

FIG. 8 shows an example embodiment according to a further aspect of thepresent invention.

FIG. 9 shows an example embodiment according to a further aspect of thepresent invention.

FIG. 10 shows a further example embodiment according to an aspect of thepresent invention.

FIG. 11 shows a further example embodiment according to an aspect of thepresent invention.

REFERENCE NUMBERS

10 gas burner

12 support or flange

14 central gas inlet port

16 gas supply or mixing chamber

18 end cap

20 burner deck

22 perforated metal plate

24 perforation

30 perforation

MODE(S) FOR CARRYING OUT THE INVENTION

Examples of a burner according to the present invention will bedescribed with reference to FIGS. 1 to 11.

FIG. 1 shows a gas burner 10, preferably a premix burner, comprising asupport or flange 12 which has a central gas inlet port 14 for supply ofgas into a gas supply or mixing chamber 16. The gas supply chamber 16 isenclosed by a perforated metal plate 22. The perforated metal plate 22is connected at the bottom to the support or flange 12 through a basesection. The perforations 24 in the perforated metal plate 22 providethe burner deck 20. The burner deck 20 has an overall porosity which isequal to or lower than 11%, preferably lower than 10%, even morepreferably lower than 9%.

FIG. 2A shows a perspective view of a burner according to the presentinvention. FIG. 2B shows a cross sectional view taken along the lineII-II′ in FIG. 2A. FIGS. 2A and 2B shows a gas burner 10, preferably apremix burner, comprising a support or flange 12 which has a central gasinlet port 14 for supply of gas into a gas supply or mixing chamber 16.The gas supply chamber 16 is enclosed by a perforated metal plate 22 andan end cap 18 substantially opposite to said gas inlet port 14. Theperforations 24 in the perforated metal plate 22 provide the burner deck20. The end cap 18 is connected to the top of the perforated metal plate22 and the perforated metal plate 22 is connected at the bottom to thesupport or flange 18 through a base section. The burner deck 20 has anoverall porosity which is equal to or lower than 11%, preferably lowerthan 10%, even more preferably lower than 9%. In an exemplaryembodiment, a burner 10, with a perforation pattern as shown in FIG. 2C,has a length of 102.4 mm and diameter of 70.4 mm. The burner deck has alength of 81.2 mm and has a porosity of 7.7%. The perforation pattern inthe perforated plate is a combination of slits and round holes. For athickness of the perforated plate of 0.6 mm, the slits being 4.0×0.5 mm,the holes having a diameter of 0.8 mm. The perforations are grouped in apattern of 4.8 mm and this pattern is repeated over the burner deck inan equal division. As explained above, this burner still needed ananti-noise device, but no pressure divider or distributor anymore.

A further aspect of the present invention provides a burner 10 whereinthe end cap 18 is also provided with perforations. FIG. 3 shows anexemplary burner according to the present invention wherein the end capis provided with perforations 30. The burner deck of this burner is asshown by reference number 20.

A further aspect of the present invention provides a burner 10 with aburner deck wherein more than 50% of the burner deck has a porositybeing equal to or lower than 9% and wherein 10 to 50% of the burner deckhas a porosity being higher than 11%. The burner deck has an overallporosity which is equal to or lower than 11%. In an exemplaryembodiment, a burner 10 as shown in FIG. 4 has a length of 94.8 mm anddiameter of 70.4 mm. The burner deck 20 has a length of 93.6 mm. Theperforation pattern in the perforated plate 22 is a combination of slitsand round holes. The thickness of the perforated plate 22 is 0.6 mm, theslits being 4.0×0.5 mm, the holes having a diameter of 0.8 mm. Theperforations are grouped in a pattern as shown in FIG. 4, wherein thefirst 11.8 mm of the burner deck length has a porosity of 15%,thereafter is a zone of 46.8 mm of the burner deck length with aporosity of 7.3% and the last zone with a length of 5.8 mm of the burnerdeck length having a porosity of 16.5%. This pattern is repeated overthe burner deck on the circumference of the burner. This provides aburner deck which has an overall porosity of 9.8%. This modification ofthe perforation pattern of the burner deck provided a burner which, nextto the effect of the deletion of the diffuser and the removal of thehumming noise, also had a more stable response on the second and higherHelmholtz or instable acoustic resonances of the heat exchanger, whichtherefore made that the burner did not provoke a whistling soundanymore. Next to that, during start sequences under cold conditions, thehumming sound was eliminated and therefore the use of anti-noise devicesin the mixing chamber of the burner could be omitted. Furthermore, thisprovided a stabilized deck over the full operating range of high to lowCO2's, and for a broad range of gas qualities. Furthermore, for thisspecific example of FIG. 4, the use of the relatively high porosity atthe beginning and end of the burner deck 20 provide an even more stableflame pattern of the burner.

An example embodiment according to a further aspect of the claimedinvention provides a gas burner with a perforated metal plate 22 with aperforation pattern as shown in FIG. 5. The shown perforation pattern isrepeated over the circumference of the burner. Here the burner deck 20has different patterns of perforations. Adding more patterns withdifferent pitches showed an increased stability for a broader range ofgas qualities and induced less NOx-emissions. The exemplary perforationpattern of FIG. 5 is an abrupt and stepwise variation of the perforationpattern in the burner deck 20.

FIG. 6 shows another example of a perforation pattern of burner deck 20according to a preferred aspect of the present invention, wherein theporosity of the burner deck 20 decreases stepwise in downstreamdirection. The shown perforation pattern is repeated in the perforatedmetal plate 22 over the circumference of the burner.

FIG. 7 shows an example of a perforation pattern of burner deck 20according to a preferred aspect of the present invention, wherein theporosity is gradually increasing. This perforation pattern is repeatedin the perforated metal plate 22 over the circumference of the burner.

FIG. 8 shows an exemplary perforation pattern of the burner deck 20,which is repeated lengthwise over the perforated metal plate 22.

FIG. 9 shows a further exemplary perforation pattern which is repeatedon the circumference of a burner. The perforation pattern is such thatno repeat of pattern is occurring along the length of the burner deck20. An exemplary burner with a length of 91.2 mm and diameter of 70.4mm. The burner deck has a length of 70.4 mm. The perforation pattern inthe perforated plate 22 is a combination of slits and round holes asshown in FIG. 9. For a thickness of the perforated plate 22 of 0.6 mm,the slits being 4.0×0.5 mm, the holes having a diameter of 0.8 mm, thisburner deck has an overall porosity of 7.5%.

The person skilled in the art will acknowledge that any perforationpattern or set of perforation patterns can be repeated lengthwise orover the circumference to obtain the burner according to the presentinvention.

Another preferred embodiment of the present invention is shown in FIG.10. The burner 10 made out of perforated metal plate 22 has a completelyrandom perforated burner deck 20 with no repeatability over the fullheight or circumference of the burner deck which provides a stabilizeddeck without the additional devices as mentioned above.

FIG. 11 shows another exemplary embodiment of the present invention.This burner has a perforated end cap 24 with different perforationpattern than the perforated metal plate 22. The perforations 30 togetherwith the perforations 24 provide the burner deck 20.

Thus there has been described a gas burner, preferably a premix burner,comprising a support which has a central gas inlet port for supply ofgas into a gas supply chamber. The gas supply chamber is enclosed by aperforated metal plate and an end cap substantially opposite to said gasinlet port. The perforations in the perforated metal plate provide aburner deck. The end cap is connected to the top of the perforated metalplate and the perforated metal plate is connected at the bottom to thesupport through a base section. The burner deck has an overall porositywhich is equal to or lower than 11%. The present invention also providesuse of this burner, e.g. in heat exchangers.

1-11. (canceled)
 12. A gas burner, preferably a premix burner,comprising a support having a central gas inlet port for supply of gasinto a gas supply chamber, said gas supply chamber being enclosed by aperforated metal plate, said perforated metal plate connected at thebottom to said support through a base section, said perforation in saidperforated metal plate providing a burner deck, characterised in thatsaid burner deck has an overall porosity being equal to or lower than11%.
 13. A gas burner, as in claim 12, said burner further comprising anend cap substantially opposite to said gas inlet port, said end capbeing connected to said perforated metal plate.
 14. A gas burner as inclaim 13, wherein said end cap is also provided with perforations, saidperforations thereby enlarging said burner deck.
 15. A gas burner as inclaim 12, wherein more than 50% of the burner deck has a porosity beingequal to or lower than 9% and wherein up to 50% of the burner deck has aporosity being higher than 11%.
 16. A gas burner as in claim 12, whereinsaid burner deck has different patterns of perforations.
 17. A gasburner as in claim 16, wherein said burner deck has at least twodifferent patterns of perforations.
 18. A gas burner as in claim 16,wherein said burner deck has a gradually changing porosity.
 19. A gasburner as in claim 16, wherein said burner deck has a substantiallycompletely random porosity.
 20. Use of the gas burner as in claim 12, ina heat exchanger.
 21. Use of the gas burner as in claim 12, in a furnaceor air heater.
 22. A gas burner, preferably a premix burner, comprisinga support having a central gas inlet port for supply of gas into a gassupply chamber, said gas supply chamber being enclosed by a perforatedmetal plate thereby eliminating a gas diffuser between the gas inletport and the perforated metal plate, said perforated metal plateconnected at the bottom to said support through a base section, saidperforation in said perforated metal plate providing a burner deck,characterised in that said burner deck has an overall porosity beingequal to or lower than 11%.